Broadband data transmission supports high bandwidth throughput through the use of multiple channels over a single transmission medium at one time. Multiple channels are supported on the single transmission medium through frequency division multiplexing. Broadband data transmission technologies include Integrated Services Digital Network (ISDN) and Asymmetric Digital Subscriber Line (ADSL).
ADSL is a new modem technology that converts existing twisted-pair telephone lines into access paths for multimedia and high speed data communications. ADSL supports data rates of up to 8 Mbps downstream to the user and up to 1.5 Mbps upstream from the user. An ADSL circuit connects an ADSL modem on each end of a twisted-pair telephone line, creating three information channels, a high speed downstream channel, a medium speed upstream channel, and a plain old telephone service (POTS) channel.
Current ADSL modems that support ATM network technology require sufficient processing and memory resources in order to perform the necessary ATM signaling procedures and segmentation and reassembly (SAR) functionality. In addition, in order to support a point-to-paint protocol for connecting a client system to the Internet, ADSL modems require sufficient processing and memory resources to run a Layer Two Tunneling Protocol (L2TP) over a User Datagram Protocol/Internet Protocol. The L2TP enables Internet service providers to operate virtual private networks (VPNs). FIG. 1 illustrates the modules that a conversational ADSL modem 100 supports in providing PPP/ATM services to a client computer system 160. The ADSL modem 100 supports a UDP/IP stack 110 and a L2TP stack 120 on a first side that is connected to the client computer system 160 via modem-client connection 150. The ADSL modem 100 also supports an ATM protocol stack 130 on a second side connected to the ADSL physical interface 140. The ATM protocol stack 130 includes an ATM layer 131, segmentation and re-assembly layer (SAR) 132, ATM adaptation layer (ML) 133, and a signaling (SIG) layer 134. Data received from the ADSL physical interface 140 us processed by the ATM protocol stack 130 on the ADSL modem 100 to retrieve raw data from the payload of an ATM cell. Similarly, data received from the client computer system 160 to be transmitted on the ADSL physical interface 140 is processed by the ATM protocol stack 130 on the ADSL modem 100 to appropriately format the data into ATM cells.